Synthetic lubricating oil



March 23, 1954 R. K. sTRATFoRD x-:r Ai. 2,673,175 SYNTHETIC LUBRICATINGOIL Filed April 21, 1951 TIME-MINUTES MEA N/NG OF SYMBOLS MCL. J0M/D-CoA/TWEA/T Louocw SIAE. m GRADE MCL 3o M/D-CONT/NEA/ cubo/v S.A.E.3o GQADE C'WO COLUMBIA/V WEBSTEQ L/GHTEQ THAN SAE. -IO GRADE CW 30COLUMe/A/v WEBSTEQ SAE 3o GQADE 5o//oo PFFE. D/sr (Mc/ pA QA PF/,v D/sr/LLATE 0F 5o SUS V/scoS/TY ATJOOE FROM M/D-CONT/^/ENT LoL/DOM CQUDE.

rf cza A. Stuart ZJZZL'czrn. A. Jones 5 ave labors' Patented Mar. 23,1954 2,673,175 SYNTHETIC LUBRICATIN G OIL Reginald K. William A. FrankA.

to Standard Oil Develop poration of Delaware Stratford, Corunna, Jones,Sarnia, Stuart, Richmond, Calif., assignors ment Company, a cor-Ontario, and Ontario, Canada, and

Application April 21, 1951, Serial No. 222,172

14 Claims.

This invention relates to the manufacture of a synthetic lubricating oilof improved properties by chemical treatment of a refined minerallubricating oil fraction.

The invention will be described hereinafter with reference to theaccompanying drawing, the single ligure of which is a graphicalillustration of the relative utility of various oils for the purposes ofthe present invention.

In the operation of internal combustion en gines, particularly atrelatively low crankcase and cooling jacket temperatures, deposition ofvarnish on piston surfaces, oil screen and other engine parts is aserious problem. This varnish deposition which is mainly caused by thefuel and varies with the type of fuel used as well as with engineoperating conditions, may be controlled by lubricants which have highsolubility for oxi dized fuel combustion products and/or preventdeposition of insoluble polymerization products. It is a well-knownpractice to add oxidation inhibitors to oil in order to preventlubricating cil oxidation in high temperature operation. Suchinhibitors, however, generally do not lessen varnish formation from fuelproducts in low temperature operation and, in fact, sometimes increasethe amount of varnish formation. In order to keep sludge and insolublematter in suspension it is a common practice to use agents known asdetergents in combination with inhibitors. In general, detergentadditives do not increase the solvent power of the lubricant for varnishforming materials. Hence the concentrations generally used do not giveeffective reduction of varnish deposits.

By the present invention, the mineral lubricating oil is submitted tochemical treatment before addition of antioxidant, if the latter isrequired. The resulting product not only keeps suspended material insuspension but also inhibits formation of insoluble varnish. At the sametime the chemical treatment gives a product of higher viscosity than theoriginal mineral oil. Thus, by the treatment it is possible to increasethe viscosity to that desired for lubricating purposes, without thenecessity of adding thickeners or without employing more expensive basestocks, such as bright stocks. Products obtained by the process of thepresent invention have shown marked ability to prevent deposition ofvarnish when employed in the crankcase of a typical automobile engine,operating under conditions at which varnish formation is heavy whenmineral lubricants and a deposit forming fuel are used.

"Briey, the process of the present invention involves the treatment of'a phenol extracted, hydronished mineral lubricating oil with oxygen toproduce a material having a saponication number of at least 20,substantially reducing the neutralization number of the resultingproduct by means of a neutralizing agent, and preferably though notalways necessarily adding to the neutralized product an antioxidant toprevent further oxidation. Whether or not an antioxidant is necessary isdependent on the nature of the base stock processed and the manner ofoxidation.

The method of the invention may be applied generally to distillates inthe viscosity range from heavy gas oil (30 seconds viscosity Saybolt atF.) to heavy lubricating oil distillates (3000 seconds Saybolt at 100F). For example, distillates from Mid-Continent (Londen) and Colombiancrudes have been found to be quite suitable.

It is considered necessary, prior to oxidation, to apply phenolextraction and mild hydrogenation to the base oil, for the purpose ofobtaining a material which oxidizes rapidly without the formation of oilinsoluble sludge. Dewaxing may also be applied, but this is notessential. The scope of the process is not limited however to the use ofphenol extraction and mild hydrogenation as the method of preparing' abase oil suitable for oxidation. It is considered possible by properchoice of conditions to produce a suitable base stock by refining thelubricating oil distillate by means of other extracting solvents such asfurfural, cresols, nitrobenzene, etc. and hydronishing or by fuming acidtreatment or by treatment with silica gel or by severe hydrogenationfollowed by mild hydrogenation.

The solvent extracted distillate may be hydrogenated, preferably by theuse of nickel, nickel on kieselguhr, platinum or palladium catalysts,but it is also possible to use sulfur resistant catalysts, such asnickel-tungsten sulldes, cobalt molybdate or alumina, molybdenum onalumina and other known hydrogenation catalysts. The dev gree ofhydrogenation necessary and the hydrogenation conditions depend on thenature of the distillate being refined and the degree of extrac tion towhich it has been subjected. lt is desirable but not absolutelynecessary to decrease the sulfur content of the oil to 0.03% or lowerand to improve the color to about 18 Robinson or better by thehydrogenation process.

The oxidation step is carried out by passing oxygen or air into the oil,preferably through a diffuser placed in the oil contained in a tall foroxidation. is .from about F., although it is possible Vto carry out theoxidation satisfactorily in the temperature range from about 200 toabout 400 F. The saponication numberv is increasedLtvo approximatelyafter an absorption utf8-10% vby weight of oxygen and to approximately50460 aiter the absorption of 14-16% oxygen. Yields of oxidized materialon the basis of mineral oil charged are generally about 99 volumepercent at 20 saponiiication number and 96 volume percent at 50'saponiication value. The exact chemical nature of the saponiiiablematerial cannot be defined from the data at present available.

In the present process no advantage hasbeen demonstrated for the use ofmetallic catalysts such as manganese naphthenate, calcium salts andother recommended oxidation catalysts. If metallic catalysts are used,extra processing steps may be necessary for their removal. As a catalystt`o initiate oxidation, particularly when air is used as the oxidizingagent, benzoyl peroxide has been found to be effective. `Other organicperoxides appear to be useful in a similar manner, and do not reduirethe extra processing steps which are required when metal catalysts areused.

Oxidation by means of air takes place much more slowly of course thanwith gaseous oxygen. Whereas a hydronished Mid-Continent Loudenstock-was `converted by commercial oxygen at 350 F. into a materialhaving a saponication number of -30 in 45 minutes, similar treatment ofthis stock at the same temperature with air required 54 hours to producea similar result. Oxidation was accomplished by means of air at 400 F.in 16 hours, but the product was very dark in color. The addition of 1%benzoyl peroxide as catalyst in the air treatment at 300 F. produced anoxidized 'product of 43 saponiiication number in 4 hours.

Following the oxidation step, which produces an acidic product, a basicmaterial is added to substantially reduce the acidity. yGenerally theamount oi' neutralizing agent which is addedis that which istheoretically suicient to reduce the neutralization number to 0. Inactual practice a zero neutralization value has notbeen obtained byusing the theoretical quantity of basic material. However, a certaindegree oi acidity can be tolerated. The addition of the theoreticallyrequired amount of neutralizing agent has been formation. The preferred`those of 3 to Y tion temperature.

found to give a product which is non-corrosive to iron and babbit attemperatures up to 350 F. It is desirable to reduce the originalneutralization number, as determined by ASTM Method D663-46T, o theoxidizedproduct to a value not greater than one-half the original value.In the average case the neutralization number of the product should/notbe greater than about 6. However, a good product has` been obtained byoxidizing sufficiently toraise the neutralization numberto about4 21 andthen treating ywith 'a neutralizing agent (butyl alcohol) in at least 4and preferably greater than theoretical quantity even though the finalneutralization number was 9.4. It appears to be necessary to reduce theneutralization number by at least half, and preferably more than half.,Y

As neutralizing agents alcohols, such as butyl alcohol, as well asmetallic bases have been used. The alcohol has the advantage of notintroducing metallic constituents into the oil, and even where metalbases are used alcohol is useful for partially reducing highneutralization value in order to avoid the necessity of adding anundesirably large amount of 'metallic bases. Metallic bases, such as theoxides and hydroxides or" alkaline earth metals, are then used asneutralizing agents. These give a product which has the ability to keepsolid sludge and water in suspension.

For this purpose, calcium hydroxide in combination with calcium oxidehas been used, the purpose of the calcium oxide being to react Vwith thewater formed by the action of calcium hydroxide. Similarly, bariumhydroxide with and.

without barium oxide has been used. Magnesium hydroxide and/or oxide isalso believed to be suitable. Sodium and aluminum hydroxides were notfound to be satisfactory because vof a thickening action on the product.

The practice in using volatile alcohols suchw'as butyl is to heatoxidized material with 5 to 10 times as much alcohol 'as `istheoretically required for complete reduction of the neutralizationvalue by esteriilcation. During the heating period part of the alcoholis'gradually distilled oi in order to remove water and promoteesterification. Organic amines and ammonia may be employed in place oialcohols. Any oi the aliphatic saturated alcohols of 2 8 carbon ratomsare preferred.

The practice in using metallic bases with or without priorneutralization by alcohol -is to add the calculated theoretical amountof the base to the oxidized material, and to heat preferably to about15G-250 F. with agitation until all the neutralizing material dissolves.The Ymetallic base may be added 'gradually or all at once.

'After partial 'or complete reduction of the neutralization value byesteriiication and/or interaction with calcium hydroxide or othersuitable metallic bases, final traces kof alcohol and/or low boilingoxidation products including water are removed from the oxidizedmaterial by Vacuum distillation. In the laboratory vacuum distillationhas been carried out `at 5-10 mm. pressure andthe distillate takenoverhead until the still temperature reaches L15G-500 F. Lower or higherpressures may be employed provided the corresponding adjustment is madein the final distilla- Exact choice o distillation conditions depends onthe viscosity and boiling range of the original distillate. After vacuumdistillation the yield of material which is not carried overhead isgenerally about 94-95 volume percent of a product v,with 50 saponicationnumber. Yields are 96-97 volume percent of oxidized product when it hasa saponication number of about 20. Aiter vacuum stripping, the oxidizedand neutralized oil isn preferably ltered to remove any suspendedmaterial. When pure calcium hydroxide and pure calcium oxide are used asneutralizing agents no suspended material is formed and filtration isnot necessary. ,A

Itv is considered necessary to add to theufinal product an Vantioxidantin, suilicientmamountuto reduce the tendency to further oxidation by anto 20 carbon atoms may be used;V

amount which will prevent oxygen absorption at 350 F. at a greater ratethan about 1% per hour, as determined by an oxygen absorption testconducted as follows: 10 cc. of oil is placed in a closed tube fittedwith an oxygen disperser, immersed in the oil. The tube is placed in abath maintained at 350 F. and connected to a bur-ette containing oxygen.Oxygen is cirdulated through the oil at a rate of 750 inl/min. Theamount of oxygen in the burette is measured at intervals and the rate ofoxygen uptake plotted against A satisfactory oil shows only a slow rateof oxygen absorption which does not increase with time.

Any of the well k abl oxidant is the reaction product of a-pinene andphosphorus pentasulfide. Other suitable antioxidants are the alkalineearth metal salts of alkylated phenol sulfides and their reactionproducts with sulfur and suldes of phosphorus, also phenyla-naphthylamine and 2,6di-tert.butyl 4-methylphenol. The last two arerecommended for use only where the oil is not subjected to temperaturesgreater than 300 F.

In the :following table are given typical inspecweight percent of 50%lyst. After four hours nickel on kieselguhr cataat 250 F. and two hoursat 450 F. a product was obtained in 99% yield having 0.02% sulfurcontent and +26 Saybolt color. I'his product was then blown with oxygenat 350 F., whereby 14 weight percent of oxygen was absorbed after 21/2hours. A yield of 97-98 weight percent of oxidized product, based on theoil charge, was obtained of a light red color, having a saponicationnumber of 56 and a neutralization number of 17. The viscosity hadincreased to 533 seconds Saybolt at 100 F.

This oxidized product was heated with volume percent of butyl alcohol insuch a manner as to distill 01T approximately one-half of the alcoholover a period of 4 hours. The balance of the alcohol was then distilledoff by heating the mixture to 450 F. under 10 mm. vacuum. By thistreatment the neutralization value was reduced to 10. The residue fromthe distillation was then heated for six hours with 0.3% calciumhydroxide and 0.15% calcium oxide. After this treatment all the calciumhydroxide and calcium oxide had dissolved in the oil and theneutralization number was reduced to 6. The oil was ltered to remove anysuspended undissolved material, but practically no residue was obtainedon the tions of an oil after the various treatments demien The productafter neutralization, when scribed above, the Original Oils beingMid-COII- blown with oxygen at 350 F., absorbed approxitinent Loudenstocks which have been phenol mately 1.4 weight percent after one hour.1.0% extracted and hydronished. of a commercial oxidation inhibitor(reaction n "Mm" I Oil Desi Vis. Sep. Neat. Anilino Oxygen Absorptionnationg Tleatment (wirr f l' I No. No. reim (350 F.) MM .In Extractedhydmnished iight 150 95 nu J nu l 21s 9%111 one-naifhour,

lube distillate. A2 A1 after absorption oi l2-14% 533 04 56 17 156 4% inono hour.

oxygen. A3 A2 refluxed with outyl alcohol. 603 80 45 6 154 1.4%in onehour.

heated with 0.5% lime at 200 F., l0 hours vacuum stripped, i filtered.A4 A3+l%reaction product a-pinene 650 82 45 6 157 0.6%inonehour.

+P B1 Extracted hydronishcd light-l 364 95 nil nil 228 7%inone-haliliourintermediate lube distillate. B2 B1 after absorption of 8-10% 620 7823.4 7.0 195 5.5% in onehour.

Oxygen. B3 B2 heated With 0.4% lime at 200 596 S9 I 17 3.0 190 6 hoursvacuum stripped, filtered. B4 B13- 511% reaction product ar-piuenc 60289 19.5 2.4 197 0.8%inoi1el1our.

S5. C1 Mediizim grade refined distillate C2 C1 highly oxidized 547 G4. 168. 3 21 159 C3 C2 reliuxed with butyl alcohol, 555 70 70 10 148 heatcdwith 0.5% lime at 200 F., 10 hrs. vacuum stripped, filtered. C4 Same asC3+l% commercial anti- 596 70 70 9. 4 148 oxidant.

In the following examples the preparations of some satisfactory iinishedproducts are described in detail, including an engine test of the same,but it is to be understood that these examples are given by way ofillustration only and do not limit the scope of the invention.

Example 1 g oil distillate of 165 viscosity (Say- F'., obtained from aMid-Continent A lubricatin bolt) at 100 drogenation at 100 lbs/sq. in.pressure using 10 product of a-pinene and Pass) was then added, and theinhibited oxidized oil when blown with oxygen at 350 F. absorbed only0.8 weight percent after 3 hours.

The product and 45 brake horsepower, at a block temperature of F. and anoil sump temperature of F., using a deposit forming fuel.

011s were rated by a demerit system,

given a rating of 0, while a rating of 10 is given to the worstcondicted on that surface, with respect to the deposition of varnish onthe piston surfaces., The non-oxidized oil showed a demerit of 5.5-6.5,while the oxidized and neutralized oil showed a demerit of 0.5 which isquitel satisfactory. The oil` pan and oil screen of the engine operatedon the oxidized lubricant was clean and free of sludge, while thenonoxidized lubricant gave an appreciable quantity of watery sludge andthe oil screen was heavily coated with varnish.

Example 2 A light lubricating oil distillate and an intermediatelubricating oil distillate, derived from a Mid-Continent Louden crude,were separately phenol extracted and dewaxed as in Example 1. These wereblended to a viscosity of 364 seconds Saybolt at 100 F. and treated forfour hours at 350 F. and for one hour at 450 F. with hydrogen at 100lbs/sq. in. pressure in the presence of weight'percent of 50% nickel onkieselguhr catalyst. The hydrogenated product had a color of 23 Robinsonand a sulfur content of 0.02 weight percent. When blown with oxygen at340 F. it absorbed approximately 9 weight percent after l hour to give a99 volume percent yield of a light red colored product having asaponication number of 23, a neutralization number of 7, and a viscosityof 628 seconds Saybolt at 100 F.

The oxidized material was heated and shaken at intervals for 6 hours at200 F. with 0.3 weight percent calcium hydroxide and 0.1 weightrpercentcalcium oxide. By this treatment the neutralization value was reduced to3. The product was then vacuum stripped to give a 97 volume percentyield. This partially neutralized oxidized oil was then inhibited with1.0% of the reaction product of e-pinene and P285, thereby lowering theoxygen absorption rate from 2.0% in 1 hour to 0.8% in 1 hour or 1.5% in3 hours. The oil prepared in this manner was tested in a Chevroletengine in the manner described in Example 1, and a sample of theunoxidized oil, also with inhibitor, was likewise tested. The unoxidizedoil showed a piston varnish demerit rating, of 5.5-6.5, while theoxidized oil showed a demerit of 1.7. In this case also the engineoperated on the oxidized oil and had a much cleaner crankcase and oilscreen than when operated with the unoxidized oil.

It is not possible at this time to give all the exact specifications forthe oil to be oxidized but, in general, it is preferable to use an oilwhich is low in sulfur and nitrogen. These elements, along with oxygenand other materials commonly found in trace proportions, affect theoxidation rate appreciably and, therefore, affect the final productmaterially. The presence of small amounts of oxidation inhibitors,natural. or synthetic, may effectively inhibit oxidation and/or causesludge formation during oxidation. Thus in one experiment, proportionsas low as 0.01% sulfur in the form of mercaptan or aliphatic disulfidecausedl sludge formation in a closed static oxidation system (Slighoxidation at 392 FJ. By extracting the same oil with a solvent (furfuralor phenol) and then hydrofinishing, the same base stock was readilyoxidized without sludge formation.

Hence the oil should be renned tosuch a degree that it can be oxidizedreadily to a saponification number of to '70 without substantialformation of sludge or oil insoluble gums. Oils of low average molecularweight, containing about 40% ofv aromatic constituents, appear to giveoil insoluble gums and, in general, those of lower aromatic contentappearmora suitable.. Also,

oils capableof rapid oxidation are desirable. The drawing whichaccompanies this specification shows the oxidation rates for hydronishedoils of various origins and viscosity grades, as determined by a test inwhich the volume of pure oxygen absorbed at 200 C. and approximatelyatmospheric pressure is measured, using both4 10 cc. and cc. oil sampletubes in the tests. Oils which absorb 800 cc. of oxygen per 10 cc. ofoil in a period of not more than 100 minutes are especially desirablefor the purposes of this invention.

Oils treated according to the present process may be oxidized to variousdegrees, but those treated to a saponication number ranging lbetween 20a-nd 30 are particularly preferred for economic reasons. This productshould be neutralized to as low a final neutralization number asispracticable, but various products having neutralization numbers of 4, 7,17, 21, reduced to 1.4, 2.4, 6 and 9.4 upon treatment with basic reagentall showed reasonably good results.

Obviously, the degree and conditions of oxidation and neutralization andthe agents or combinations of agents employed for neutralization may bevaried within the limits previously suggested. The iinal products may befurther modified by addition of conventional modifiers such as variousantioxidants, viscosity index improvers, pour point depressants, metaldeactivators, detergents, thickeners, soaps (to form greases, forexample), as will be obvious to those skilled in the art.

What is claimed is:

1. A lubricating oil composition prepared by contacting a solventextracted, hydrogenated mineral lubricating oil fraction with a gascomprising free oxygen at a temperature of 20C-400 F. until a producthaving a saponication number of at least 20 and not more than about '70is produced, and treating the oxidized product with a neutralizing agentuntil the neutralization number of the same is reduced by at least 50%of its original value, said product having the property of inhibitingsludge and varnish formation in internal combustion engines operatingVfor extended periods at low temperatures on deposit forming gasolines.

2. A product according to'claim l obtained from a lubricating oilfraction which is hyf drogenated prior to oxidation in order to reducethe sulfur content to a value not greater than 0.03% by weight, toincrease the color to a value of at least 18 Robinson, and tosubstantially increase the oxidation rate.

3. A product according to claim 1 obtained by treatment of the oil withoxygen or a gas containing free oxygen at a temperature of 275-400 F.

4. A product according to claim 1 in which benzoyl peroxide is used ascatalyst to initiate oxidation by the gas which comprises free oxygen.

5. A process which comprises treating a solvent extracted mineral baselubricating oil of low sulfur, low nitrogen, and moderately low aromaticcontent vwith a gas comprising oxygen at a temperature range between 200and 400 F. for a period of time and under catalyst conditions such` thata saponication value of at least 20 and not more than '70 is reached,then treating the oxidized oil with aneutralizing agent consisting atleast in part of an alcohol capable of esterifying the oxidationproduct,.the product after neutralization being,I heated tor remove by 9distillation any portions which have boiling points lower than 350 F. at10 mm. pressure.

6. A process according to claim in which the neutralizing agent is amixture of calcium hydroxide and calcium oxide.

7. A process according to claim 5 in which the neutralization isaccomplished by iirst re fluxing with butyl alcohol and then bytreatment with a mixture of calcium hydroxide and calcium oxide.

8. A process which comprises contacting a phenol extracted hydrogenatedlubricating oil fraction with oxygen at a temperature of 275400 F. untila product having a saponiiication number of 20 to 70 is produced,heating the oxidized product with volume percent of butyl alcohol untilapproximately one half of the alcohol is distilled off over a period ofabout l hours, iurther heating to remove the remainder of the unreaotedalcohol at a temperature of 450 F. and 10 mm. pressure, heating theproduct for about 6 hours in the presence of 0.3 weight percent calciumhydroxide and 0.15 Weight percent calcium oxide, and adding to the nalproduct 1.0 Weight percent of an oxidation inhibitor in suil'icientamount to reduce the oxygen absorption rate at 350 F. of the product toless than 1% per hour.

9. Process according to claim 8 wherein the oil is oxidized to asaponication number of about 50.

10. Process according to claim 8 wherein the oil is oxidized to asaponication number of to 30.

11. A product extracted hydrogenated mineral lubricating oil fractionwith a gas containing free oxygen at a temperature of 200-400 F. until aproduct having a saponication number of at least 20 and not more than isproduced, treating the oxidized product with a neutralizing agent untilthe neutralization number of the same is reduced to not more than 50% ofits original value and in any case to a Value not greater than preparedby contacting a phenol 12. A product according to claim 11. to which hasbeen added an antioxidant sufficient in amount to prevent oxygenabsorption when the oil is in contact with oxygen at 350'D F. at a ratenot greater than 1% per hour.

13. A product according to claim l1, prepared by partially neutralizingthe oxygenated product with butyl alcohol and further neutralizing witha mixture of calcium hydroxide and calcium oxide.

14. A product prepared by extracting a lubricating oil distillate ofabout 165 seconds viscosity Saybolt at F., obtained from a parainic typecrude oil, with phenol to give 5 an extracted oil having a viscosityindex of at least 95, deyvaxing the extracted oil to a pour point ofabout 0 F., hydrogenating the extracted, dewaxed oil until the samecontains not more than 0.02% sulfur, blowing the hydrogenated oil withoxygen at about 350 F. until about 14 weight percent of oxygen has beenabsorbed, heating the oxidized oil with butyl alcohol until theneutralization number is reduced by at least half and in any case untilit is not greater than 10, heating the partially neutralized productwith a mixture of calcium hydroxide and calcium oxide until theneutralization number was reduced to not greater than 6, and adding tothe oil product a suilicient amount of an antioxidant to preventabsorption of oxygen when the oil is in contact with oxygen at 350 F. ata rate greater than l weight percent per hour.

REGINALD K. STRATFORD. WILLIAM A. JONES. FRANK A. STUART.

References Cited in the le of this patent UNTED STATES PATENTS NumberName Date 2,070,627 Shoemaker Feb. 16, 1937 2,455,337 Jones Nov. 310,1948 2,560,650 Kronstein July 17, 1951

1. A LUBRICATING OIL COMPOSITION PREPARED BY CONTACTING A SOLVENTEXTRACTED, HYDROGENATED MINERAL LUBRICATING OIL FRACTION WITH A GASCOMPRISING FREE OXYGEN AT A TEMPERATURE OF 200-400* F. UNTIL A PRODUCTHAVING A SAPONIFICATION NUMBER OF AT LEAST 20 AND NOT MORE THAN ABOUT 70IS PRODUCED, AND TREATING THE OXIDIZED PRODUCT WITH A NEUTRALIZING AGENTUNTIL THE NEUTRALIZATION